1. Field of the Invention
The invention concerns a rotating unit of a medical imaging device (in particular a computed tomography apparatus) with a hydrostatic slide bearing and an integrated coolant conduit. Furthermore, the invention concerns a medical imaging device (in particular a computer tomography apparatus) with such a rotating unit.
2. Description of the Prior Art
Computed tomography is a diagnostic method that is widely used in medical engineering. In such a method, a region of a patient or subject that is to be examined is exposed slice-by-slice with radiation, and exposures of the region of the subject or patient that is to be examined are acquired from various directions. An image reconstruction from the acquired exposures subsequently enables a two-dimensional or three-dimensional depiction of the examined region and contributes to the production of a diagnosis.
The computed tomography apparatuses that are used for this typically have a frame that has a stationary part and a part that can be tilted as necessary. The frame has at least one stationary part and is designed as a supporting structure of a rotatable part of the computed tomography apparatus. The rotating part has an acquisition system that includes at least one detector and at least one radiation source. The stationary part thereby forms a stator and the rotatable part forms a rotor. The rotor is borne in the stator by a bearing so that it may rotate, and the two parts form a rotating unit. The rotating part of the computed tomography apparatus has an essentially annular or cylindrical shape with a continuous central opening or a tunnel, and can be rotated around the axis of symmetry of this opening or of this tunnel. The radiation source and the detector thereby define a measurement region in which a subject or patient can be positioned so as to be movable. The detector and the radiation source are typically situated on diametrically opposite sides of the central opening. The detector thereby rotates with the radiation source around the rotation axis of the rotating part along which the subject or the patient is moved. Between the frame (thus the stationary part) and the rotatable part, a rotation bearing is formed that enables the rotation of the rotatable part relative to the stationary part. It is additionally possible that the entire rotating unit, composed of at least the rotation bearing, the rotor and stator, is designed so as to be able to tilt.
Computed tomography examinations require a very precise arrangement of the entire medical apparatus (in particular of the at least one acquisition system), which is directly linked with the image quality. Modern computed tomography apparatuses presently also have rotation speeds of up to approximately 240 min−1 (revolutions per minute). Higher rotation speeds are also conceivable in the future, for example in the range of up to 400 min−1.
Therefore, high mechanical demands are placed on such medical devices. Conventional, rotating units predominantly have a roller bearing in different embodiments (for example a ball bearing) between the rotor and the stator, wherein the rotation of the rotor is driven by a drive bearing or a direct drive, for example.
However, such a roller bearing is subject to a wear and must be serviced regularly (in particular be re-lubricated), which means a high service cost. Due to the wear, such a roller bearing has a limited lifespan. Moreover, a large amount of heat energy is released (in particular from the radiation source) during the operation of a computed tomography apparatus, which can likewise negatively affect the lifespan of such bearings by changing the contact pressure due to the thermal conductivity and the material expansion. Such rotation bearings are also sensitive to dust particles that if they reach the bearing surface, destroy the track of the roller body and additionally reduce the lifespan of the bearing. Such bearings are also sensitive to shocks or vibrations, such that the bearings must accordingly be protected (in particular during transport) with complicated protective measures. Moreover, the noise level of such bearings increases drastically with increasing rotation speed, so measures having high production and installation costs are required in order to bring the noise level to a level that is not disruptive, in particular for the patient and/or for the operating personnel.